Morphology of PI–PEO block copolymers for lithium batteries

Abstract

Polyimide (PI)–polyethylene oxide (PEO) block copolymers have a wide variety of applications in microelectronics, since PI–PEO films exhibit a high degree of thermal and chemical stability. The polymers consist of short, rigid rod T-shaped PI segments, alternating with flexible, PEO coil segments. The highly incompatible PI rods and PEO coils should phase-separate, especially in the presence of lithium ions used as electrolytes for lithium polymer batteries. The rigid rod phase provides a high degree of dimensional stability. In this paper, we provide evidence by DSC that the self-assembled ordered structure of the PI–PEO molecules is formed from concentrated solution rather than the bulk state. Tapping mode AFM and X-ray diffraction are applied to observe the nanodomains in the phase separation of the PI and PEO before and after doping with lithium ions. In addition, we report evidence of the ion transport primary mechanism, in the amorphous phase of the lithium salt-doped PI–PEO block copolymers' multinuclear NMR linewidth, spin-lattice relaxation time, and pulsed field gradient diffusion measurements.